Method and device for transmitting information for client cooperation in wireless communication system

ABSTRACT

Provided are a method and a device for transmitting information for client cooperation in a wireless communication system. A first device or a base station of the client cooperation determines whether the first device is operable as a cooperative device for the client cooperation, on the basis of a decision factor. The first device transmits information for carrying out the client cooperation to a second device on the basis of whether the first device is operable as the cooperative device for the client cooperation.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to wireless communication and, moreparticularly, to a method and device for transmitting information forclient cooperation in a wireless communication system.

2. Related Art

In next generation multimedia mobile communication systems, which havebeen actively studied in recent years, there is a demand for a systemcapable of processing and transmitting a variety of information (e.g.,video and radio data) in addition to the early-stage voice service.Further, a 3rd generation wireless communication system is followed by a4th generation wireless communication which is currently being developedaiming at supporting a high-speed data service of 1 gigabits per second(Gbps) in downlink and 500 megabits per second (Mbps) in uplink. Thewireless communication system is designed for the purpose of providingreliable communication to a plurality of users irrespective of theirlocations and mobility. However, a wireless channel has an abnormalcharacteristic such as a fading phenomenon caused by a path loss, noise,and multipath, an inter-symbol interference (ISI), a Doppler effectcaused by mobility of a user equipment, etc. Therefore, varioustechniques have been developed to overcome the abnormal characteristicof the wireless channel and to increase reliability of wirelesscommunication.

Meanwhile, with the advent of a ubiquitous environment, there is a rapidincrease in a demand for receiving a seamless service anytime anywhereby using equipments. In order to satisfy such a demand, a clientcooperation technique may be introduced in a wireless communicationsystem. The client cooperation technique refers to a technique by whicha specific device helps transmission of another device. That is, onedevice may directly communicate with a base station (BS) or mayindirectly communication with the BS by the aid of another device. Theclient cooperation technique has an effect of lower power consumption,throughput enhancement, etc.

The client cooperation technique can be more effectively used in amulti-radio access technology (RAT) device. The multi-RAT device refersto a device that can operate in a plurality of communication systems.For example, the multi-RAT device can operate both in institute ofelectrical and electronics engineers (IEEE) 802.16m and IEEE 802.11. Toprovide an easiness access to the BS anytime anywhere and to maintaineffective performance, the multi-RAT device can use a multi-RAT clientcooperation technique (i.e., improved tethering) in a heterogeneousnetwork.

It is necessary to newly define procedures for performing, by themulti-RAT device, the multi-RAT client cooperation techniqueautonomously without aid of the BS.

SUMMARY OF THE INVENTION

The present invention provides a method and apparatus for transmittinginformation for client cooperation in a wireless communication system.The present invention proposes a method for determining whether a devicecan operate as a cooperative device of client cooperation for performingmulti-radio access technology (RAT) client cooperation, and a method fortransmitting information for the client cooperation to the other device.

In an aspect, a method for transmitting information for clientcooperation in a wireless communication system is provided. The methodincludes determining whether a first device is operable as a cooperativedevice of client cooperation based on decision factors, and transmittinginformation for performing the client cooperation to a second devicebased on whether the first device is operable as the cooperative deviceof the client cooperation.

Whether the first device is operable as the cooperative device of theclient cooperation may be determined by the first device or by a basestation (BS).

The decision factors may include at least one of a movement speed of thefirst device, a location of the first device, the presence and absenceand a number of cooperative device candidates around the first device,power reserves of the first device, and a channel state between thefirst device and a BS.

The method may further include exchanging information on the decisionfactors with the BS.

Whether the first device is operable as the cooperative device of theclient cooperation may be triggered by the second device.

The information for performing the client cooperation may include atleast one of information on whether the first device is a multi radioaccess technology (RAT) device, a type of a system to which the firstdevice is connected, whether the first device is operable as thecooperative device of the client cooperation, information on a networkservice provider (NSP) supported by a BS, and system information of theBS.

The system information of the BS may include at least one of anidentifier of the BS, cell bar information, a media access control (MAC)version, and a network configuration.

The information for the client cooperation may not include the otherremaining information, when the first device is not the multi-RAT deviceor when the first device is not operable as the cooperative device ofthe client cooperation.

Whether the first device is the multi-RAT device or whether the firstdevice is operable as the cooperative device of the client cooperationmay be indicated by a service set identifier (SSID).

The information for performing the client cooperation may be transmittedthrough at least one of a beacon frame, a probe response frame, anauthentication response frame, an association response frame, and a dataframe.

The probe response frame may be a response to a probe request frametransmitted by the second device, and the probe request frame mayinclude a client cooperation request for the first device.

The authentication response frame may be a response to an authenticationrequest frame transmitted by the second device, and the authenticationrequest frame may include a client cooperation request for the firstdevice.

The association response frame may be a response to an associationrequest frame transmitted by the second device, and the associationrequest frame may include a client cooperation request for the firstdevice.

In another aspect, a method for determining performing of clientcooperation in a wireless communication system is provided. Te methodincludes receiving information for performing client cooperation from afirst device, determining whether the client cooperation with the firstdevice can be performed based on the received information for performingthe client cooperation, attempting network entry to a base station (BS),when the client cooperation with the first device can be performed, andnewly seeking a different device for the client cooperation, when theclient cooperation with the first device cannot be performed.

In another aspect, a device in a wireless communication system isprovided. The device includes a radio frequency (RF) unit configured totransmit or receive a radio signal, and a processor connected to the RFunit, and configured to determine whether a first device is operable asa cooperative device of client cooperation based on decision factors,and transmit information for performing the client cooperation to asecond device based on whether the first device is operable as thecooperative device of the client cooperation.

A BS and a multi-RAT device can efficiently communicate with each otherthrough client cooperation technology.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a wireless communication system.

FIG. 2 shows an example of a frame structure of IEEE 802.16m.

FIG. 3 shows an example of a state machine of a UE in an initial networkentry process in IEEE 802.16m.

FIG. 4 shows an example of a state machine of a BS in an initial networkentry process in IEEE 802.16m.

FIG. 5 shows an example of a frame structure of IEEE 802.11.

FIG. 6 shows an example of implementing a client cooperation technique.

FIG. 7 shows another example of implementing a client cooperationtechnique.

FIG. 8 shows another example of implementing a client cooperationtechnique.

FIG. 9 shows an embodiment of the proposed network entry method.

FIG. 10 shows another embodiment of the proposed network entry method.

FIG. 11 shows another embodiment of the proposed network entry method.

FIG. 12 shows an embodiment of the proposed method for transmittinginformation for client operation.

FIG. 13 shows another embodiment of the proposed method for transmittinginformation for client cooperation.

FIG. 14 shows an embodiment of the proposed method for transmittinginformation for client cooperation.

FIG. 15 shows another embodiment of the proposed method for transmittinginformation for client cooperation.

FIG. 16 shows another embodiment of the proposed method for transmittinginformation for client cooperation.

FIG. 17 shows another embodiment of the proposed method for transmittinginformation for client cooperation.

FIG. 18 shows another embodiment of the proposed method for transmittinginformation for client cooperation.

FIG. 19 is a block diagram showing wireless communication system toimplement an embodiment of the present invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

A technology below can be used in a variety of wireless communicationsystems, such as code division multiple access (CDMA), frequencydivision multiple access (FDMA), time division multiple access (TDMA),orthogonal frequency division multiple access (OFDMA), and singlecarrier frequency division multiple access (SC-FDMA). CDMA can beimplemented using radio technology, such as universal terrestrial radioaccess (UTRA) or CDMA2000. TDMA can be implemented using radiotechnology, such as global system for mobile communications(GSM)/general packet radio service (GPRS)/enhanced data rates for GSMevolution (EDGE). OFDMA can be implemented using radio technology, suchas IEEE 802.11(Wi-Fi), IEEE 802.16(WiMAX), IEEE 802-20, or Evolved UTRA(E-UTRA). IEEE 802.16m is the evolution of IEEE 802.16e, and it providesa backward compatibility with an IEEE 802.16e-based system. UTRA is partof a universal mobile telecommunications system (UMTS). 3rd generationpartnership project (3GPP) long term evolution (LTE) is part of evolvedUMTS (E-UMTS) using evolved-UMTS terrestrial radio access (E-UTRA), andit adopts OFDMA in downlink (DL) and SC-FDMA in uplink (UL). LTE-A(advanced) is the evolution of 3GPP LTE.

IEEE 802.16m and IEEE 802.11 are chiefly described as an example inorder to clarify the description, but the technical spirit of thepresent invention is not limited to IEEE 802.16m and IEEE 802.11.

FIG. 1 shows a wireless communication system.

Referring to FIG. 1, the wireless communication system 10 includes oneor more base stations (BSs) 11. The BSs 11 provide communicationservices to respective geographical areas (in general called ‘cells’) 15a, 15 b, and 15 c. Each of the cells can be divided into a number ofareas (called ‘sectors’). A user equipment (UE) 12 can be fixed ormobile and may be referred to as another terminology, such as a mobilestation (MS), a mobile terminal (MT), a user terminal (UT), a subscriberstation (SS), a wireless device, a personal digital assistant (PDA), awireless modem, or a handheld device. In general, the BS 11 refers to afixed station that communicates with the UEs 12, and it may be referredto as another terminology, such as an evolved-NodeB (eNB), a basetransceiver system (BTS), or an access point.

The UE generally belongs to one cell. A cell to which a UE belongs iscalled a serving cell. A BS providing the serving cell withcommunication services is called a serving BS. A wireless communicationsystem is a cellular system, and so it includes other cells neighboringa serving cell. Other cells neighboring the serving cell are calledneighbor cells. A BS providing the neighbor cells with communicationservices is called as a neighbor BS. The serving cell and the neighborcells are relatively determined on the basis of a UE.

This technology can be used in the downlink (DL) or the uplink (UL). Ingeneral, DL refers to communication from the BS 11 to the UE 12, and ULrefers to communication from the UE 12 to the BS 11. In the DL, atransmitter may be part of the BS 11 and a receiver may be part of theUE 12. In the UL, a transmitter may be part of the UE 12 and a receivermay be part of the BS 11.

FIG. 2 shows an example of a frame structure of IEEE 802.16m.

Referring to FIG. 2, a superframe (SF) includes a superframe header(SFH) and four frames F0, F1, F2, and F3. Each frame may have the samelength in the SF. Although it is shown that each SF has a length of 20milliseconds (ms) and each frame has a length of 5 ms, the presentinvention is not limited thereto. A length of the SF, the number offrames included in the SF, the number of SFs included in the frame, orthe like can change variously. The number of SFs included in the framemay change variously according to a channel bandwidth and a cyclicprefix (CP) length.

One frame includes 8 subframes SF0, SF1, SF2, SF3, SF4, SF5, SF6, andSF7. Each subframe can be used for uplink or downlink transmission. Onesubframe includes a plurality of orthogonal frequency divisionmultiplexing (OFDM) symbols in a time domain, and includes a pluralityof subcarriers in a frequency domain. An OFDM symbol is for representingone symbol period, and can be referred to as other terminologies such asan OFDM symbol, an SC-FDMA symbol, etc., according to a multiple accessscheme. The subframe can consist of 5, 6, 7, or 9 OFDMA symbols.However, this is for exemplary purposes only, and thus the number ofOFDMA symbols included in the subframe is not limited thereto. Thenumber of OFDMA symbols included in the subframe may change variouslyaccording to a channel bandwidth and a CP length. A subframe type may bedefined according to the number of OFDMA symbols included in thesubframe. For example, it can be defined such that a type-1 subframeincludes 6 OFDMA symbols, a type-2 subframe includes 7 OFDMA symbols, atype-3 subframe includes 5 OFDMA symbols, and a type-4 subframe includes9 OFDMA symbols. One frame may include subframes each having the sametype. Alternatively, one frame may include subframes each having adifferent type. That is, the number of OFDMA symbols included in eachsubframe may be identical or different in one frame. Alternatively, thenumber of OFDMA symbols included in at least one subframe of one framemay be different from the number of OFDMA symbols of the remainingsubframes of the frame.

Time division duplex (TDD) or frequency division duplex (FDD) may beapplied to the frame. In the TDD, each subframe is used in uplink ordownlink transmission at the same frequency and at a different time.That is, subframes included in a TDD frame are divided into an uplinksubframe and a downlink subframe in the time domain. A switching pointrefers to a point where a transmission direction is changed from anuplink region to a downlink region or from a downlink region to anuplink region. In the TDD, the number of the switching points in eachframe may be two. In the FDD, each subframe is used in uplink ordownlink transmission at the same time and at a different frequency.That is, subframes included in an FDD frame are divided into an uplinksubframe and a downlink subframe in the frequency domain. Uplinktransmission and downlink transmission occupy different frequency bandsand can be simultaneously performed.

One OFDMA symbol includes a plurality of subcarriers. The number ofsubcarriers is determined by a fast Fourier transform (FFT) size. Thesubcarrier can be classified into a data subcarrier for datatransmission, a pilot subcarrier for various estimations, and a nullsubcarrier for a guard band and a direct current (DC) carrier. The OFDMAsymbol is characterized by parameters BW, N_(used), n, G, etc. Theparameter BW denotes a nominal channel bandwidth. The parameter N_(used)denotes the number of used subcarriers (including the DC subcarrier).The parameter n denotes a sampling factor. The parameter n is combinedwith the parameters BW and N_(used) to determine a subcarrier spacingand a useful symbol time. The parameter G denotes a ratio of a cyclicprefix (CP) time and a useful time.

Table 1 below shows an orthogonal frequency division multiple access(OFDMA) parameter.

TABLE 1 Channel bandwidth, BW(MHz) 5 7 8.75 10 20 Sampling factor, n28/25 8/7 8/7 28/25 28/25 Sampling frequency, F_(s)(MHz) 5.6 8 10 11.222.4 FFT size, N_(FFT) 512 1024 1024 1024 2048 Subcarrier spacing,Δf(kHz) 10.94 7.81 9.77 10.94 10.94 Useful symbol time, T_(b)(μs) 91.4128 102.4 91.4 91.4 G = ⅛ Symbol time, T_(s)(μs) 102.857 144 115.2102.857 102.857 FDD Number of 48 34 43 48 48 ODFMA symbols per 5 msframe Idle time(μs) 62.857 104 46.40 62.857 62.857 TDD Number of 47 3342 47 47 ODFMA symbols per 5 ms frame TTG + RTG(μs) 165.714 248 161.6165.714 165.714 G = 1/16 Symbol time, T_(s)(μs) 97.143 136 108.8 97.14397.143 FDD Number of 51 36 45 51 51 ODFMA symbols per 5 ms frame Idletime(μs) 45.71 104 104 45.71 45.71 TDD Number of 50 35 44 50 50 ODFMAsymbols per 5 ms frame TTG + RTG(μs) 142.853 240 212.8 142.853 142.853 G= ¼ Symbol time, T_(s)(μs) 114.286 160 128 114.286 114.286 FDD Number of43 31 39 43 43 ODFMA symbols per 5 ms frame Idle time(μs) 85.694 40 885.694 85.694 TDD Number of 42 30 38 42 42 ODFMA symbols per 5 ms frameTTG + RTG(μs) 199.98 200 136 199.98 199.98 Number of Guard Left 40 80 8080 160 subcarriers Right 39 79 79 79 159 Number of used subcarriers 433865 865 865 1729 Number of PRU in type-1 subframe 24 48 48 48 96

In Table 1, N_(FFT) denotes a smallest power of 2 greater than N_(used).A sampling factor is defined as F_(s)=floor(n·BW/8000)×8000. Asubcarrier spacing is defined as Δf=F_(s)/NFFT. A useful symbol time isdefined as T_(b)=1/Δf. A CP time is defined as T_(g)=G·T_(b). An OFDMAsymbol time is defined as T_(s)=T_(b)+T_(g). A sampling time is definedas T_(b)/N_(FFT).

FIG. 3 shows an example of a state machine of a UE in an initial networkentry process in IEEE 802.16m.

First, the UE acquires system information. If set DL synchronization,received DL and UL parameters, and a network are not selected (100),system information is acquired again. If set DL synchronization,received DL and UL parameters, and a network are selected (101), the UEwaits for a ranging opportunity. When a ranging opportunity is obtained(110), the UE transmits an initial ranging code.

The UE waits for an AAI-RNG-ACK message or a CDMA allocation A-MAPinformation element (IE). If a timer T3 or T31 has expired or anAAI-RNG-ACK message in a state “not detected” is received and a retryopportunity has expired or an AAI-RNG-ACK message in a state “abort” isreceived (120), the UE acquires system information again. Alternatively,if an AAI-RNG-ACK message in a state “continue” or “not detected” isreceived or a timer T3 or T31 has expired and a retry opportunityremains (121), the UE waits for a ranging opportunity. When a CDMAallocation A-MAP IE is received (122), the UE transmits an AAI-RNG-REQmessage.

After transmitting the AAI-RNG-REQ message, the UE waits for anAAI-RNG-RSP message with a temporary station identifier (STID). If thetimer T3 has expired and the retry opportunity has been exhausted or anAAI-RNG-RSP message in a state “abort” is received (130), the UEacquires system information again. If the timer T3 has expired and theretry opportunity still remains (131), the UE waits for a rangingopportunity. When an AAI-RNG-RSP message with an STID of a state“success” is received (132), the UE transmits an AAI-SBC-REQ message.

After transmitting the AAI-SBC-REQ message, the UE waits for anAAI-SBC-RSP message. If a timer T18 has expired and the retryopportunity has been exhausted or an AAI-RNG-RSP message in a state“abort” is received (140), the UE acquires system information again. Ifthe timer T18 has expired and the retry opportunity remains (141), theUE transmits an AAI-SBC-REQ message. If an AAI-SBC-RSP message isreceived and authorization is supported (142), UE authorization and akey exchange are performed. Here, if a timer T17 has expired and theretry opportunity has been exhausted or the AAI-RNG-RSP message in astate “abort” is received (150), the UE acquires system informationagain. If the UE is authorized (151), the UE transmits an AAI-REG-REQmessage. If an AAI-SBC-RSP message is received and authorization is notsupported (143), the UE transmits an AAI-REG-REQ message.

The UE that has transmitted the AAI-REG-REQ message waits for anAAI-REG-RSP message with an STID. Here, if a timer T6 has expired andthe retry opportunity has been exhausted or an AAI-RNG-RSP message or anAAI-RES-CMD message in a state “abort” is received (160), the UEacquires system information again. If the timer T6 has expired and theretry opportunity remains (161), the UE transmits an AAI-SBC-REQmessage. When an AAI-REG-RSP message is received (162), the UE processesthe AAI-REG-RSP message.

A basic service flow is configured and network entry is completedthrough the above process. Here, when the AAI-RNG-RSP message, theAAI-DREG-RSP message, or the AAI-RES-CMD message in a state “abort” isreceived (170), the UE acquires system information again.

FIG. 4 shows an example of a state machine of a BS in an initial networkentry process in IEEE 802.16m.

The BS waits for an initial ranging code. The BS receives the initialranging code and transmits an AAI-RNG-ACK message in a state “continue”(200). Alternatively, the BS receives the initial ranging code andtransmits an AAI-RNG-ACK message in a state “success” and a CDMAallocation A-MAP IE (201). Alternatively, the BS receives the initialranging code and transmits an AAI-RNG-ACK message in a state “abort”(209). Here, an initial network entry process is terminated.

After transmitting the AAI-RNG-ACK message in a state “success” and theCDMA allocation A-MAP IE, the BS waits for an AAI-RNG-REQ message. TheBS receives an AAI-RNG-REQ message and transmits an AAI-RNG-RSP messagein a state “success” with a temporary STID (210). Alternatively, if aranging response processing time has expired (219), the initial networkentry process is terminated.

After transmitting the AAI-RNG-RSP message in a state “success” with atemporary STID, the BS waits for an AAI-SBC-REQ message. In thisprocess, the BS may receive the AAI-RNG-REQ message again and transmitthe AAI-RNG-RSP message again (220). If the AAI-SBC-REQ message isreceived and UE authorization is supported (221), the BS performs UEauthorization and a key exchange. In this process, the BS may receivethe AAI-SBC-REQ message again and transmit the AAI-SBC-RSP message again(230). If the UE is authorized (231), the BS waits for an AAI-REG-REQmessage. Alternatively, the BS may terminate the initial network entryprocess by transmitting an AAI-RNG-RSP message in a state “abort” (229and 239). If the AAI-SBC-REQ message is received and UE authorization isnot supported (222), the BS waits for an AAI-REG-REQ message.

If UE authorization is not supported while waiting for the AAI-REG-REQmessage, the BS may receive the AAI-SBC-REQ message again and transmitthe AAI-SBC-RSP message again (240). When the AAI-REG-REG message isreceived, the BS transmits an AAI-REG-RSP message with an STID (241).Alternatively, the BS may terminate the initial network entry process bytransmitting an AAI-RNG-RSP message in a state “abort” or an AAI-RES-CMDmessage (249).

After transmitting the AAI-REG-RSP message with an STID, the BS waitsfor acknowledgement (ACK) for the AAI-REG-RSP message. In this process,the BS may receive the AAI-REG-REQ message again and transmit theAAI-REG-RSP message with an STID again (250). When implicit or explicitACK for the AAI-REG-RSP message is received (251), a connection is setup and the initial network entry is completed. Alternatively, the BS mayterminate the initial network entry process by transmitting anAAI-RNG-RSP message, an AAI-RES-CMD message, or an AAI-DREG-RSP messagein a state “abort” (259, 269).

FIG. 5 shows an example of a frame structure of IEEE 802.11.

A frame of IEEE 802.11 includes a set of fields in a fixed order.Referring to FIG. 5, the frame of IEEE 802.11 includes a frame controlfield, a duration/ID field, an address 1 field, an address 2 field, anaddress 3 field, a sequence control field, an address 4 field, a qualityof service (QoS) control field, an HT control field, a frame body field,and a frame check sequence (FCS) field. Among the fields listed above,the frame control field, the duration/ID field, the address 1 field, andthe FCS field constitute a minimum IEEE 802.11 frame format, and may beincluded in all IEEE 802.11 frames. The address 2 field, the address 3field, the sequence control field, the address 4 field, the QoS controlfield, the HT control field, and the frame body field may be includedonly in a specific frame type.

The frame control field may include various subfields. The duration/IDfield may be 16 bits in length. The address field may include a basicservice set identifier (BSSID), a source address (SA), a destinationaddress (DA), a transmitting STA address (TA), and a receiving STAaddress (RA). In the address field, different fields may be used forother purposes according to a frame type. The sequence control field canbe used when fragments are reassembled or when an overlapping frame isdiscarded. The sequence control field may be 16 bits, and may includetwo subfields indicating a sequence number and a fragment number. TheFCS field can be used to check an error of a frame received by astation. The FCS field may be a 32-bit field including a 32-bit cyclicredundancy check (CRC). An FCS can be calculated across the frame bodyfield and all fields of a media access control (MAC) header.

The frame body field may include information specified for an individualframe type and subtype. That is, the frame body field carries high-leveldata from one station to another station. The frame body field can alsobe called a data field. The frame body field can be variously changed inlength. A minimum length of the frame body field may be zero octet. Amaximum length of the frame body field may be determined by a total sumof a maximum length of a MAC service data unit (MSDU), a length of amesh control field, and an overhead for encryption or a total sum of amaximum length of an aggregated MSDU (A-MSDU) and an overhead forencryption. The data frame includes high-level protocol data of theframe body field. The data frame may always include the frame controlfield, the duration/ID field, the address 1 field, the address 2 field,the address 3 field, the sequence control field, the frame body field,and the FCS field. A presence of an address 4 field may be determined bya configuration of a ‘To DS’ subfield and a ‘From DS’ subfield in theframe control field. Another data frame type can be categorizedaccording to a function.

A management frame may always include the frame control field, theduration/ID field, the address 1 field, the address 2 field, the address3 field, the sequence control field, the frame body field, and the FCSfield. Data included in the frame body field generally uses afixed-length field called a fixed field and a variable-length fieldcalled an information element. The information element is avariable-length data unit.

The management frame can be used for various purposes according to asubtype. That is, a frame body field of a different subtype includesdifferent information. A beacon frame reports an existence of a network,and takes an important role of network maintenance. The beacon framecorresponds to a parameter which allows a mobile station to participatein the network. In addition, the beacon frame is periodicallytransmitted so that the mobile station can scan and recognize thenetwork. A probe request frame is used to scan an IEEE 802.11 network inwhich the mobile station exists. A probe response frame is a responsefor the probe request frame. An authentication request is used so thatthe mobile station requests an access point to perform authentication.An authentication response frame is a response for the authenticationrequest frame. A deauthentication frame is used to finish anauthentication relation. An association request frame is transmitted sothat the mobile station participates in the network when the mobilestation recognizes the compatible network and is authenticated. Anassociation response frame is a response for the association requestframe. A deassociation frame is used to finish an association relation.

Three states may exist according to an authentication and associationprocedure in IEEE 802.11. Table 2 below shows the three states of IEEE802.11.

TABLE 2 Authentication Association State 1 X X State 2 ◯ X State 3 ◯ ◯

To transmit a data frame, a device must perform the authentication andassociation procedure with respect to a network. In Table 2, a procedureof transitioning from the state 1 to the state 2 can be called theauthentication procedure. The authentication procedure can be performedin such a manner that one device acquires information of a differentdevice and authenticates the different device. The information of thedifferent device can be acquired by using two methods, i.e., a passivescanning method for acquiring information of a different node byreceiving a beacon frame and an active scanning method for acquiring theinformation of the different device by transmitting a probe requestmessage and receiving a probe response message received in responsethereto. The authentication procedure can be complete by exchanging anauthentication request frame and an authentication response frame.

In Table 2, a procedure of transitioning from the state 2 to the state 3can be called the association procedure. The association procedure canbe complete when two devices exchange the association request frame andthe association response frame upon completion of the authenticationprocedure. An association ID can be allocated by the associationprocedure.

A client cooperation technique may be introduced in a wirelesscommunication system. One device may directly communicate with a basestation (BS) or may indirectly communication with the BS by the aid ofanother device. Hereinafter, a source device refers to a device whichcommunicates with the BS through a connection with another device. Acooperative device refers to a relay entity which helps the sourcedevice to communicate with the BS. The client cooperation technique hasan effect of lower power consumption. In terms of a device, a path-losscan be decreased by the client cooperation technique, thereby being ableto decrease transmit power. In terms of a network, total network powerconsumption can be decreased. In addition, the client cooperationtechnique has an effect of throughput enhancement. In terms of a device,a source device can use a good-quality link between a cooperative deviceand a BS and between BSs. In addition, an antenna extension gain can beobtained. In terms of the network, network capacity can be increased byusing client clustering based on frequency reuse without an additionalinfrastructure.

FIG. 6 shows an example of implementing a client cooperation technique.

Referring to FIG. 6, in the client cooperation technique, a sourcedevice can directly communicate with a macro BS, or can communicate withthe macro BS via a cooperative device. The cooperative device maydirectly communicate with the macro BS, or can help communication of thesource device. This is different from a mobile relay in a sense that thesource device can directly communicate with the macro BS. In this case,each device and the macro BS can communicate by using a first radioaccess technology (RAT), and the source device and the cooperativedevice can communicate by using a second RAT. The first RAT may be aradio technology such as IEEE 802.16 (WiMAX), IEEE 802.16m or IEEE802.20, etc. Alternatively, the first RAT may be a radio technology suchas E-UTRA, 3GPP LTE or 3GPP LTE-A, etc. The second RAT may be IEEE802.11.

FIG. 7 shows another example of implementing a client cooperationtechnique.

The client cooperation technique can be more effectively used in amulti-RAT device. The multi-RAT device refers to a device that canoperate in a plurality of communication systems. For example, themulti-RAT device can operate both in IEEE 802.16m and IEEE 802.11. Whenthe multi-RAT device uses the client cooperation technique, themulti-RAT device can communicate with an IEEE 802.16m BS by using aplurality of RATs. For example, as shown in FIG. 7, if channel qualityis poor between a second device and a BS or if the second device locatedin a shadow area cannot receive a signal from the BS, the first devicecan be used as a cooperative device to communicate with the BS. In thiscase, each device and the BS can communicate by using the first RAT, andthe source device and the cooperative device can communicate by usingthe second RAT. The first RAT may be a radio technique such as IEEE802.16, IEEE 802.16m, IEEE 802.20, E-UTRA, 3GPP LTE or 3GPP LTE-A, etc.The second RAT may be IEEE 802.11.

FIG. 8 shows another example of implementing a client cooperationtechnique.

A source device and a macro BS (e.g., IEEE 802.16m BS) can be connectedthrough a direct link, and can be connected through an indirect link byusing a cooperative device. In this case, each device and the BS can beconnected by using IEEE 802.16m, and the source device and thecooperative device can be connected by using IEEE 802.11.

Hereinafter, a method for a source device to perform network entry to abase station (BS) through a cooperative device will be described. Asource device may perform network entry to a BS by transmitting varioustypes of messages for network entry to the BS through a cooperativedevice. Hereinafter, it is assumed that the source device and thecooperative device are connected through IEEE 802.11 and the cooperativedevice and the BS are connected through IEEE 802.16m, as shown in FIGS.7 and 8. However, the embodiment of the present inventions concept isnot limited thereto and may be applicable to various radio accesstechnologies (RATs). Based on the proposed method, the source device maybe connected to the IEEE 802.16m BS through IEEE 802.11 connection withthe cooperative device.

The method for the source device to perform network entry to the BSthrough the cooperative device may be divided into two methods.

1) First, the source device may attempt network entry to the IEEE802.16m BS, without obtaining information for performing multi-RATclient cooperation (hereinafter, referred to as ‘client cooperation’,)from a counterpart device. Namely, a method in which the source deviceperforms network entry to the IEEE 802.16m BS without knowing whetherthe counterpart device is operable as a cooperative device after thesource device completes authentication and association procedure withthe counterpart device may be proposed. In this case, since it cannot beknown yet whether the counterpart device is operable as a cooperativedevice in client cooperation, the counterpart device may not be called acooperative device. The counterpart device may not be called acooperative device until when it is confirmed that the counterpartdevice is operable as a cooperative device.

FIG. 9 shows an embodiment of the proposed network entry method.

In step S300, the source device transmits a ranging request (RNG-REQ)message for network entry to the counterpart device in the IEEE 802.16msystem. Here, the RNG-REQ message may be encapsulated in a frame bodyfield of an IEEE 802.11 frame and transmitted.

In step S301, the counterpart device may transmit an acknowledgement(ACK) message for the RNG-REQ message to the source device. Transmissionof the ACK message may be optional. When the counterpart device isoperable as a cooperative device of client cooperation, the counterpartdevice may transmit the ACK message to the source device. Namely, thecounterpart device may accept that it will operate as a cooperativedevice of client cooperation, through the ACK message. Accordingly, thecounterpart device may become a cooperative device of clientcooperation, and the source device may be a source device of clientcooperation. Also, when it is assumed that an ACK message should benecessarily transmitted with respect to the RNG-REQ message, if thesource device fails to receive an ACK message during a specific periodof time after it transmits the RNG-REQ message, the source device maydetermine that a client cooperation request has been rejected, and mayseek a different counterpart device.

In step S310, the counterpart transfers the RNG-REQ message to the BS byusing a general ranging procedure or a general bandwidth requestprocedure. In step S311, the BS transmits a ranging response (RNG-RSP)message as a response to the RNG-REQ message to the counterpart device.Here, the BS may include a new identifier used for client cooperation oran identifier allocated to the source device in a header or an extendedheader, and transmit the same. Based on the corresponding identifier,the counterpart device may recognize that the RNG-RSP message is to betransmitted to the source device, and may transmit the RNG-RSP messageas is, without decoding it, to the source device.

In step S320, the counterpart device transmits the RNG-RSP message tothe source device. Here, the RNG-RSP message may be encapsulated in aframe body field of an IEEE 802.11 frame and transmitted. Upon receivingthe RNG-RSP message as a response to the RNG-REQ message the sourcedevice has transmitted, the source device may recognize that thecounterpart device has accepted to operate as a cooperative device ofclient cooperation. Accordingly, the counterpart device may become acooperative device of client cooperation, and the source device may be asource device of client cooperation. Also, after the source devicetransmits the RNG-REQ message, if it fails to receive the RNG-RSPmessage during a specific period of time, the source device maydetermine that the client cooperation request was rejected, and may seeka different counterpart device.

In a manner similar to that described above, the source device maynegotiate basic capability with the IEEE 802.16m BS. Namely, the sourcedevice encapsulates a basic capability request (SBC-REQ) message in aframe body field of an IEEE 802.11 frame and transmits the same to acounterpart device, and the counterpart device transmits the SBC-REQmessage to the BS on the basis of a general bandwidth request procedure.As a response to DL resource allocation information using DL assignmentA-MAP, or the like, and the SBC-REQ message, the BS transmits a basiccapability response (SBC-RSP) message to the counterpart device. Thecounterpart device encapsulates the received SBC-RSP message in a framebody field of an IEEE 802.11 frame and transmits the same to the sourcedevice.

The other remaining network entry procedures, than the ranging and thebasic capability negotiation, may be performed in a similar manner,except for exchanged messages. For example, a registration procedure maybe performed in a manner similar to that of the basic capabilitynegotiation procedure as described above. However, messages exchangedbetween and among the source device, the cooperative device, and the BSare a registration request (REG-REQ) message and a registration response(REG-RSP) message. Here, the BS may include a new identifier used forclient cooperation or an identifier assigned to the source device in aheader or an extended header and transmit the same. A privacy keymanagement procedure may also be performed in a manner similar to thatof the basic capability negotiation procedure. However, messagesexchanged between or among the source device, the cooperative device,and the BS are privacy key management-related messages. A dynamicservice flow procedure may be performed in a manner similar to that ofthe basic capability negotiation procedure. However, messages exchangedbetween or among the source device, the cooperative device, and the BSare dynamic service flow-related messages.

2) After obtaining information for performing multi-RAT clientcooperation from the cooperative device, the source device may attemptnetwork entry to the IEEE 802.16m BS. Namely, a method in which thesource device performs network entry to the IEEE 802.16m BS aftercompleting the authentication and association procedure with thecooperative device may be proposed. The method for the source device toobtain the information for performing multi-RAT client cooperation fromthe cooperative device will be described below.

FIG. 10 shows another embodiment of the proposed network entry method.

In step S400, the source device transmits a RNG-REQ message to thecooperative device. In this case, the RNG-REQ message may beencapsulated in a frame body field of an IEEE 802.11 frame andtransmitted. Since the cooperative device has already operated as acooperative device of client cooperation, it may implicitly recognizethe received message as a RNG-REQ message.

In step S410, the cooperative device transmits a ranging code to the BS.In step S411, the BS allocates UL resource according to a generalranging procedure. In step S412, the cooperative device transmits theRNG-REQ message to the BS through the allocated UL resource. Here, inorder to inform the BS about the presence of the cooperative devicetransmitting the RNG-REQ message received from the source device, thecooperative device may transmit an identifier thereof such as a stationidentifier (STID) together with the RNG-REQ message. Here, theidentifier of the cooperative device may be included in a header, anextended header, or the RNG-REQ message, and transmitted. The BS mayrecognize the presence of the cooperative device assisting the sourcedevice which has transmitted the RNG-REQ message, through the identifierof the cooperative device.

In step S413, the BS transmits a RNG-RSP message as a response to theRNG-REQ message. The BS may transmit DL resource allocation informationusing a CDMA assignment A-MAP IE, or the like, and the RNG-RSP messageto the cooperative device according to a general ranging procedure.Here, the DL assignment information may be masked with a random accessidentifier (RAID) or the STID of the cooperative device. Also, the BSmay include a new identifier used for client cooperation or anidentifier assigned to the source device in a header, an extendedheader, or the RNG-RSP message, and transmit the same.

In step S420, the cooperative device transmits the RNG-RSP message tothe source device. Here, the RNG-RSP message may be encapsulated in aframe body field of an IEEE 802.11 frame and transmitted.

FIG. 11 shows another embodiment of the proposed network entry method.

In step S450, the source device transmits a RNG-REQ message to thecooperative device. In this case, the RNG-REQ message may beencapsulated in a frame body field of an IEEE 802.11 frame andtransmitted. Since the cooperative device has already operated as acooperative device of client cooperation, it may implicitly recognizethe received message as the RNG-REQ message.

In step S460, the cooperative device transmits a bandwidth request (BR)including its identifier to the BS. Since network entry of the sourcedevice and the BS has not been completed and the source device has notobtained an appropriate identifier yet, the identifier of thecooperative device may be used.

In step S461, the BS allocates UL resource according to a generalbandwidth request procedure. In this case, the BS does not know fromwhich device the bandwidth request has been received actually, so ascheduler of the BS may first assume that the cooperative device hasrequested the UL resource, and perform scheduling. For example, due tothe corresponding bandwidth request and approval, a bandwidth requestfrom the cooperative device may be pushed back on the priority list,since then. In order to prevent this, a BR preamble code set, a quickaccess message, or an indicator of a BR header aiming at indicating thatit is to transmit data of a different device (e.g., the source device)may be newly defined.

In step S462, the cooperative device transmits a RNG-REQ message to theBS through the allocated UL resource. The BS may decode the RNG-REQmessage to determine from which device the corresponding RNG-REQ messagehas been transmitted.

In step S463, the BS transmits a RNG-RSP message to the cooperativedevice as a response to the RNG-REQ message. The BS may transmit DLresource allocation information and the RNG-RSP message using anidentifier of the cooperative device to the cooperative device accordingto a general bandwidth request procedure. In this case, the BS mayinclude a new identifier used for client cooperation or an identifierassigned to the source device in a header, an extended header, or theranging response message and transmit the same.

In step S470, the cooperative device transmits the RNG-RSP message tothe source device. In this case, the RNG-RSP message may be encapsulatedin a frame body field of an IEEE 802.11 frame, and transmitted.

In a manner similar to that described above, the source device maynegotiate basic capability with the IEEE 802.16m. Namely, the sourcedevice encapsulates a SBC-REQ message in a frame body field of an IEEE802.11 frame and transmits the same to a counterpart device, and thecounterpart device transmits the SBC-REQ message to the BS on the basisof a general bandwidth request procedure. In response to DL resourceallocation information using DL assignment A-MAP, or the like, and theSBC-REQ message, the BS transmits a SBC-RSP message to the counterpartdevice. The counterpart device encapsulates the received SBC-RSP messagein a frame body field of an IEEE 802.11 frame and transmits the same tothe source device.

The other remaining network entry procedures, than the ranging and thebasic capability negotiation, may be performed in a similar manner,except for exchanged messages. For example, a registration procedure maybe performed in a manner similar to that of the basic capabilitynegotiation procedure as described above. However, messages exchangedbetween and among the source device, the cooperative device, and the BSare a REG-REQ message and a REG-RSP message. Here, the BS may include anew identifier used for client cooperation or an identifier assigned tothe source device in a header or an extended header and transmit thesame. A privacy key management procedure may also be performed in amanner similar to that of the basic capability negotiation procedure.However, messages exchanged between or among the source device, thecooperative device, and the BS are privacy key management-relatedmessages. A dynamic service flow procedure may be performed in a mannersimilar to that of the basic capability negotiation procedure. However,messages exchanged between or among the source device, the cooperativedevice, and the BS are dynamic service flow-related messages.

Hereinafter, a method for determining whether a counterpart device isoperable as a cooperative device will be described. Whether acounterpart device is operable as a cooperative device may be determinedby the counterpart device itself or by a BS.

FIG. 12 shows an embodiment of the proposed method for transmittinginformation for client operation. FIG. 12 shows a case in which acounterpart device determines by itself whether it is operable as acooperative device.

In step S520, a first device (candidate eligible to become a cooperativedevice) may determine whether it is operable as a cooperative device inconsideration of various decision factors such as a movement speedthereof, a location thereof, the presence and absence and a number ofdevices eligible to become a cooperative device therearound, powerconsumption thereof, a channel state with the BS, and the like. In thiscase, the decision factors based on which whether the first device isoperable as a cooperative device is determined may be obtained from theBS in step S510. Also, the determining whether the first device isoperable as a cooperative device may be triggered by a second device (acandidate eligible to become a source device) in step S500. Namely, stepS500 and step S510 may be optional.

When the first device determines that it satisfies the decision factorsaccording to the determination result, the first device informs thesecond device that it is operable as a cooperative device of clientcooperation in step S522. When the first device determines that it doesnot satisfy the decision factors, the first device informs the seconddevice that it is not operable as a cooperative device of clientcooperation in step S521. Whether the first device is operable as acooperative device of client cooperation may be simultaneously broadcastto a plurality of devices or may be transmitted to a specific device ina unicast manner.

FIG. 13 shows another embodiment of the proposed method for transmittinginformation for client cooperation. FIG. 13 shows a case in whichwhether a counterpart device is operable as a cooperative device isdetermined through triggering by a BS.

When various decision factors such as the movement speed thereof, thelocation thereof, the presence and absence and a number of deviceseligible to become a cooperative device therearound, the powerconsumption thereof, the channel state with to the BS, and the like, aresatisfied in step S550, the BS may request the first device to operateas a cooperative device in step S551.

In step S560, the first device determines whether to approve the requestfor operating as a cooperative device received from the BS. Only whenthe first device approves the request for operating as a cooperativedevice, the first device may operate as a cooperative device. If thefirst device rejects the request for operating as a cooperative deviceof client cooperation, the first device informs the BS accordingly instep S561. When the first device approves the request for operating as acooperative device of client cooperation, the first device informs theBS accordingly in step S562. Meanwhile, after the approval of thecooperative device operation request, if radio frequency (RF) power ofthe IEEE 802.11 is turned off, the first device may turn on the RF powerof IEEE 802.11 and perform a general operation performed in an IEEE802.11 system. Such a general operation may be performed constantly orperiodically. Also, as a state of the first device is changed, the BSmay release the eligibility of first device as a cooperative device.

In step S570, the second device may request the first device to confirmwhether the first device is operable as a cooperative device of clientcooperation. In step S580, the first device may make a determination onthe request from the second device as to whether to approve or rejectthe cooperation device operation request received from the BS. If thefirst device rejects the request for operating as a cooperative device,the first device cannot operate as a cooperative device, so it mayinform the second device that the first device is not operable as acooperative device in step S581. If the first device approves therequest for operating as a cooperative device, since the first device isoperable as a cooperative device, the first device may inform the seconddevice that it is operable as a cooperative device in step S582. Also,in a case in which the first device is eligible as a cooperative deviceby satisfying the decision factors but it cannot operate as acooperative device for various reasons, for example, it cannot help thesource device any longer, and the like, the first device may inform thesecond device that it is not operable as a cooperative device in stepS581.

Hereinafter, a method in which the source device obtains information forperforming client cooperation from a cooperative device will bedescribed.

First, information for performing client cooperation transmitted by thefirst device which has determined as to whether to operate as acooperative device in client cooperation with the BS will be described.

-   -   The information for performing client cooperation transmitted by        the first device may include information regarding whether the        first device is a multi-RAT device.    -   The information for performing client cooperation may include a        type of a system to which each device is connected. For example,        the information for performing client cooperation may include        information regarding whether each device is connected to IEEE        802.16m, whether each device is connected to 3GPP LTE, and the        like. In a case in which to which system each device is        connected is recognizable implicitly, the information may be        omitted. If the first device is connected to two or more types        of systems, the information for performing client cooperation        may be established for each system.    -   The information for performing client cooperation may also        include whether the first device is operable as a cooperative        device in client cooperation. Also, the information for        performing client cooperation may include whether the first        device supports multi-RAT client cooperation. Whether the first        device is operable as a cooperative device may be determined by        the first device itself or through triggering by the BS as        described above.    -   The information for performing client cooperation may include        network service provider (NSP)-related information. The        NSP-related information may include an NSP ID and a name list.    -   The information for performing client cooperation may include        system information of the BS to which the first device is        connected. The system information of the BS may be system        information transmitted through an SFH or a broadcast channel.        The system information of the BS may be limited to system        information the second device should necessarily know to        communicate with the BS. For example, the system information of        the BS included in the information for performing client        cooperation may include a BS ID (base station identifier), cell        bar information, a MAC version, network configuration        information, and the like. In a case in which a bit value        forming the cell bar information is 0b1, network entry or        reentry to a corresponding cell may not be permitted. The        network configuration information indicates a configuration of        an ABS network such as an AAI (advanced air network)        configuration, a WirlelessMAN-OFDMA network configuration, or        the like.

After the determination of whether the first device is operable as acooperative device in client cooperation, the first device and thesecond device may exchange information for performing clientcooperation. The first device may transmit information for performingclient cooperation as described hereinafter to the second devicesimultaneously in a single frame during a procedure for authenticationor association with the second device or after the association with thesecond device is completed. In this case, the single frame in which theclient cooperation performing information is transmitted may be any oneamong management frames such as a beacon frame, a probe response frame,an authentication response frame, an association response frame, and thelike, and a data frame. Alternatively, during the procedure forauthentication or association with the second device or after theassociation with the second device is completed, the first device maytransmit information for performing client cooperation as describedhereinafter to the second device through a plurality of frames. Forexample, information as to whether the first device is a multi-RATdevice may be transmitted in a beacon frame to the second device, andother information may be transmitted to the second device through anauthentication response message. Also, in a case in which the firstdevice is not a multi-RAT device or in a case in which the first deviceis not operable as a cooperative device of client cooperation, the otherremaining information may not be transmitted to the second device.

Also, among the information for performing client cooperation, theinformation regarding whether the first device is a multi-RAT device orwhether it is operable as a cooperative device may be provided through aservice set identifier (SSID) transmitted through a beacon frame or aprobe response frame. Namely, a candidate device that may become acooperative device may transmit an SSID set to a defined value inadvance through a beacon frame or a probe response frame. Upon receivingthe beacon frame or the probe response frame including the previouslydefined SSID from the first device, the second device may recognize thatthe first device is operable as a cooperative device of clientcooperation. The SSID may be defined according to a combination of radioaccess technologies (RATs). For example, when IEEE 802.16m and IEEE802.11 configure a multi-RAT, SSID may be 0x12345. In a case in whichIEEE 802.11 configures a multi-RAT, SSID may be 0x6789A.

Upon receiving the information for performing client cooperation, thesecond device determines whether performing of multi-RAT clientcooperation with the first device is proper on the basis of theinformation for performing client cooperation. For example, when thefirst device is not a multi-RAT device, the second device may determinethat performing multi-RAT client cooperation with the first device maynot be proper. Also, in a case in which the first device is not operableas a cooperative device with respect to a system to which the seconddevice intends to be connected, in a case in which the an NSP of thesecond device does not exist in received NSP information, in a case inwhich a value of cell bar information is 0b1, or in a case in which areceived MAC version does not support the second device, the seconddevice may determine that performing multi-RAT client cooperation withthe first device is not proper.

In the case in which the second device determines that performingmulti-RAT client cooperation with the first device is not proper, thesecond device may attempt to access a corresponding BS according to acharging method, a service flow forming method, a data conversionmethod, and the like. For example, in a case in which an NSP of thesecond device does not exist in received NSP information with respect toa system to which the second device intends to be connected, if aservice that may be charged to the corresponding device is providedalthough a network of a different operator who has not joined is used,the second device may attempt to access the corresponding BS.Alternatively, in a case in which a MAC version received with respect tothe system to which the second device intends to be connected does notsupport the second device, if the first device is able to processtransmitted or received data and transmit the same to an actualreceiver, the second device may attempt to access the corresponding BS.

The second device determines whether performing client cooperation withthe first device is proper. When the second device determines thatperforming client cooperation with the first device is not proper, thesecond device may seek a different device. When the second devicedetermines that performing client cooperation with the first device isproper, the second device may start network entry to the BS.

FIG. 14 shows an embodiment of the proposed method for transmittinginformation for client cooperation.

In step S600, the first device transmits a beacon frame to the seconddevice. In this case, the beacon frame includes information forperforming client cooperation between the first device and the seconddevice. In step S601, the second device determines whether performingclient cooperation with the first device is proper on the basis of thereceived information for performing client cooperation. When the seconddevice determines that performing client cooperation with the firstdevice is proper, in step S602, the first device and the second deviceperform authentication and association procedures, and the second deviceattempts network entry to the BS.

FIG. 15 shows another embodiment of the proposed method for transmittinginformation for client cooperation.

In step S610, the second device transmits a probe request frame to thefirst device. The second device requests the first device to performclient cooperation through a probe request frame. In step S611, thefirst device transmits a probe response frame to the second device. Theprobe response frame includes information for performing clientcooperation between the first device and the second device. In stepS612, the second device determines whether performing client cooperationwith the first device is proper on the basis of the received informationfor performing client cooperation. When the second device determinesthat performing client cooperation with the first device is proper, instep S613, the first device and the second device perform authenticationand authentication procedures, and the second device attempts networkentry to the BS.

FIG. 16 shows another embodiment of the proposed method for transmittinginformation for client cooperation.

In step S620, the first device transmits a beacon frame or a proberesponse frame to the second device. In step S621, the second devicetransmits an authentication request frame to the first device. Thesecond device requests the first device to perform client cooperationthrough the authentication request frame. The authentication requestframe may include information regarding a system to which the seconddevice intends to be connected. In step S622, the first device transmitsan authentication response frame to the second device. Theauthentication response frame includes information for performing clientcooperation between the first device and the second device. In stepS623, the second device determines whether performing client cooperationwith the first device is proper on the basis of the received informationfor performing client cooperation. When the second device determinesthat performing client cooperation with the first device is proper, instep S624, the first device and the second device perform an associationprocedure and the second device attempts network entry to the BS. Whenthe second device determines that performing client cooperation with thefirst device is not proper, in step S625, the first device and thesecond device perform an authentication release procedure.

FIG. 17 shows another embodiment of the proposed method for transmittinginformation for client cooperation.

In step S630, the first device transmits a beacon frame or a proberesponse frame to the second device. In step S631, the first device andthe second device perform an authentication procedure. In step S632, thesecond device transmits an association request frame to the firstdevice. The second device requests the first device to perform clientcooperation through the association request frame. The associationrequest frame may include information regarding a system to which thesecond device intends to be connected. In step S633, the first devicetransmits an association response frame to the second device. Theassociation response frame includes information for performing clientcooperation between the first device and the second device. In stepS634, the second device determines whether performing client cooperationwith the first device is proper on the basis of the received informationfor performing client cooperation. When the second device determinesthat performing client cooperation with the first device is proper, instep S635, the first device and the second device exchange messages forIEEE 802.16m network entry to attempt network entry to the BS. When thesecond device determines that performing client cooperation with thefirst device is not proper, in step S636, the first device and thesecond device perform an association release procedure.

FIG. 18 shows another embodiment of the proposed method for transmittinginformation for client cooperation.

FIG. 18 shows a case in which information for performing clientcooperation is transmitted distributedly through different frames,rather than being transmitted through a single frame simultaneously. Instep S700, the first device transmits a beacon frame or a probe responseframe to the second device. The beacon frame or the probe response framemay include a portion of the information for performing clientcooperation. In step S710, the second device determines whetherperforming client cooperation with the first device is proper on thebasis of a portion of the information for performing client cooperation.When the second device determines that performing client cooperationwith the first device is not proper, the second device seeks a differentnode (or device). When the second device determines that performingclient cooperation with the first device is proper, in step S711, thefirst device and the second device perform an authentication procedure.

In the authentication procedure, another portion of the information forperforming client cooperation may be transmitted. In step S720, thesecond device determines whether performing client cooperation with thefirst device is proper on the basis of still another portion of theinformation for performing client cooperation. When the second devicedetermines that performing client cooperation with the first device isproper, in step S721, the first device and the second device perform anassociation procedure. When the second device determines that performingclient cooperation with the first device is not proper, in step S722,the first device and the second device perform an authentication releaseprocedure, and after the completion of the authentication releaseprocedure, the second device seeks a different node.

In an association procedure, still another portion of the informationfor performing client cooperation may be transmitted. In step S730, thesecond device determines whether performing client cooperation with thefirst device is proper on the basis of the still another portion of theinformation for performing client cooperation. When the second devicedetermines that performing client cooperation with the first device isproper, in step S731, the second device exchanges messages for IEEE802.16m network entry with the first device, and attempts network entryto the BS. When the second device determines that performing clientcooperation with the first device is not proper, in step S732, the firstdevice and the second device perform an association release procedure,and after the completion of the association release procedure, thesecond device seeks a different node.

Alternatively, the information for performing client cooperation may betransmitted through a data frame after the completion of the associationprocedure between the first device and the second device.

As described above, by exchanging information for performing clientcooperation between the first device and the second device, the approvalprocedure for client cooperation may be completed. After all theprocedures are completed, the first device may operate as a cooperativedevice of client cooperation and the second device may operate as asource device of client cooperation.

FIG. 19 is a block diagram showing wireless communication system toimplement an embodiment of the present invention.

A BS 800 includes a processor 810, a memory 820, and a radio frequency(RF) unit 830. The processor 810 may be configured to implement proposedfunctions, procedures, and/or methods in this description. Layers of theradio interface protocol may be implemented in the processor 810. Thememory 820 is operatively coupled with the processor 810 and stores avariety of information to operate the processor 810. The RF unit 830 isoperatively coupled with the processor 810, and transmits and/orreceives a radio signal.

A UE 900 may include a processor 910, a memory 920 and a RF unit 930.The processor 910 may be configured to implement proposed functions,procedures and/or methods described in this description. Layers of theradio interface protocol may be implemented in the processor 910. Thememory 920 is operatively coupled with the processor 910 and stores avariety of information to operate the processor 910. The RF unit 930 isoperatively coupled with the processor 910, and transmits and/orreceives a radio signal.

The processors 810, 910 may include application-specific integratedcircuit (ASIC), other chipset, logic circuit and/or data processingdevice. The memories 820, 920 may include read-only memory (ROM), randomaccess memory (RAM), flash memory, memory card, storage medium and/orother storage device. The RF units 830, 930 may include basebandcircuitry to process radio frequency signals. When the embodiments areimplemented in software, the techniques described herein can beimplemented with modules (e.g., procedures, functions, and so on) thatperform the functions described herein. The modules can be stored inmemories 820, 920 and executed by processors 810, 910. The memories 820,920 can be implemented within the processors 810, 910 or external to theprocessors 810, 910 in which case those can be communicatively coupledto the processors 810, 910 via various means as is known in the art.

In view of the exemplary systems described herein, methodologies thatmay be implemented in accordance with the disclosed subject matter havebeen described with reference to several flow diagrams. While forpurposed of simplicity, the methodologies are shown and described as aseries of steps or blocks, it is to be understood and appreciated thatthe claimed subject matter is not limited by the order of the steps orblocks, as some steps may occur in different orders or concurrently withother steps from what is depicted and described herein. Moreover, oneskilled in the art would understand that the steps illustrated in theflow diagram are not exclusive and other steps may be included or one ormore of the steps in the example flow diagram may be deleted withoutaffecting the scope and spirit of the present disclosure.

What has been described above includes examples of the various aspects.It is, of course, not possible to describe every conceivable combinationof components or methodologies for purposes of describing the variousaspects, but one of ordinary skill in the art may recognize that manyfurther combinations and permutations are possible. Accordingly, thesubject specification is intended to embrace all such alternations,modifications and variations that fall within the spirit and scope ofthe appended claims.

What is claimed is:
 1. A method for transmitting information for clientcooperation in a wireless communication system, the method comprising:determining whether a first device is operable as a cooperative deviceof client cooperation based on decision factors; and transmittinginformation for performing the client cooperation to a second devicebased on whether the first device is operable as the cooperative deviceof the client cooperation.
 2. The method of claim 1, wherein whether thefirst device is operable as the cooperative device of the clientcooperation is determined by the first device or by a base station (BS).3. The method of claim 1, wherein the decision factors include at leastone of a movement speed of the first device, a location of the firstdevice, the presence and absence and a number of cooperative devicecandidates around the first device, power reserves of the first device,and a channel state between the first device and a BS.
 4. The method ofclaim 1, further comprising: exchanging information on the decisionfactors with the BS.
 5. The method of claim 1, wherein whether the firstdevice is operable as the cooperative device of the client cooperationis triggered by the second device.
 6. The method of claim 1, wherein theinformation for performing the client cooperation includes at least oneof information on whether the first device is a multi radio accesstechnology (RAT) device, a type of a system to which the first device isconnected, whether the first device is operable as the cooperativedevice of the client cooperation, information on a network serviceprovider (NSP) supported by a BS, and system information of the BS. 7.The method of claim 6, wherein the system information of the BS includesat least one of an identifier of the BS, cell bar information, a mediaaccess control (MAC) version, and a network configuration.
 8. The methodof claim 6, wherein the information for the client cooperation does notinclude the other remaining information, when the first device is notthe multi-RAT device or when the first device is not operable as thecooperative device of the client cooperation.
 9. The method of claim 6,wherein whether the first device is the multi-RAT device or whether thefirst device is operable as the cooperative device of the clientcooperation is indicated by a service set identifier (SSID).
 10. Themethod of claim 1, wherein the information for performing the clientcooperation is transmitted through at least one of a beacon frame, aprobe response frame, an authentication response frame, an associationresponse frame, and a data frame.
 11. The method of claim 10, whereinthe probe response frame is a response to a probe request frametransmitted by the second device, and wherein the probe request frameincludes a client cooperation request for the first device.
 12. Themethod of claim 10, wherein the authentication response frame is aresponse to an authentication request frame transmitted by the seconddevice, and wherein the authentication request frame includes a clientcooperation request for the first device.
 13. The method of claim 10,wherein the association response frame is a response to an associationrequest frame transmitted by the second device, and wherein theassociation request frame includes a client cooperation request for thefirst device.
 14. A method for determining performing of clientcooperation in a wireless communication system, the method comprising:receiving information for performing client cooperation from a firstdevice; determining whether the client cooperation with the first devicecan be performed based on the received information for performing theclient cooperation; attempting network entry to a base station (BS),when the client cooperation with the first device can be performed; andnewly seeking a different device for the client cooperation, when theclient cooperation with the first device cannot be performed.
 15. Adevice in a wireless communication system, the device comprising: aradio frequency (RF) unit configured to transmit or receive a radiosignal; and a processor connected to the RF unit, and configured to:determine whether a first device is operable as a cooperative device ofclient cooperation based on decision factors, and transmit informationfor performing the client cooperation to a second device based onwhether the first device is operable as the cooperative device of theclient cooperation.